In 2007-2008, pot experiments were conducted on cv. Michalina head lettuce grown in an unheated greenhouse in spring. The aim of the study was to compare organic and mineral iron compounds as well as their rates in terms of the efficiency of their effect on yield of lettuce and iron content in lettuce leaves. The experimental factors included: 1) sources of iron, i.e. 2 mineral – iron(II) sulfate and iron(III) sulfate, and 3 organic – iron(III) citrate, iron(II) gluconate and iron chelate Fe(III) DTPA, 2) level of iron, i.e. 6 levels – 20 (control), 45, 70, 95, 120 and 220 mg Fe dm–3 substrate. Lettuce was grown in 6 dm3 containers. Limed highmoor peat, enriched with macro- and micronutrients to meet requirements of lettuce, was used as a substrate. Each experiment included 26 combinations comprising 4 replications each. A container with 4 lettuce plants constituted one replication. Lettuce was harvested at the consumption stage. Concentrations of iron, copper, manganese and zinc were determined in plant material by ASA after wet mineralization in a mixture of acids HNO3 and HClO4 at a 3:1 ratio (v:v). The application of iron(III) sulfate, iron(II) sulfate, iron citrate or iron gluconate ranging from 45 to 220 mg Fe dm–3 and Librel Fe-DTPA chelate ranging from 45 to 120 mg Fe dm–3 did not have any significant effect on the yield of lettuce. Librel Fe-DTPA applied at a rate of 220 mg Fe dm–3 resulted in a reduction of yield. The highest Fe content (irrespectively of the applied Fe rates) in lettuce leaves was recorded after the application of Librel Fe DTPA, while the lowest one – after iron gluconate was used. When analyzing the effect of Fe levels, irrespectively of the used iron compounds, the lowest Fe content in leaves was observed in the control, growing at the levels of 45 and 70 mg Fe dm–3, as well as at 90 and 120 mg Fe dm–3 and reaching its peak after the application of 220 mg Fe dm–3.